Sensitive shunting circuits



Nov. 28, 1961 c. E. STAPLES SENSITIVE SHUNTING CIRCUITS Filed Oct. 28, 1959 Ila 7 d T 5 2 m y w H M w lm I Jw m @o m M 2 INVENT OR. Ulawfo d E Staples.

BY 10., .W.

United States Patent r 3,011,050 SENSITIVE SHUNTING CIRCUITS Crawford E. Staples, Edgewood, Pa., assiguor to Westinghouse Air Brake Company, Wilmer-ding, Pin, a corporation of Pennsylvania Filed Oct. 28, 1959, Ser. No. 849,202 12 Claims. (Cl. 246-34) My invention relates to railway track circuit apparatus and more particularly to railway track circuits providing high shunting sensitivity.

Reliable operation of a track circuit of an insulated railway track section requires that a current source not only satisfactorily energize a track relay when the section is unoccupied but also requires that such current be effectively shunted away from the associated track relay when the section is occupied. It is known that a shunt effected through the wheels and axles of a train or car varies in its resistance due to the presence, at times, of a thin coating or film of relatively high resistance on the rail and/ or wheel surfaces.

The problem of providing a satisfactory shunt is particularly complicated in automatic classification yards for various reasons. In such yards oily films are frequently encountered clue to, for example, the drippings from freshly oiled wheel bearings, brine drippings from standing cars, etc. An oily film has a tendency to spread, to

collect dirt, and to transfer from wheel to rail or vice versa depending on the temperature. This film resistance may be of such nature as to form a high resistance path to the low voltage usually employed in track circuits and such low voltage will normally not break down or puncture the I The shunting problems are made more difiicult in track circuits used for classification yards since the track sections employed are normally so short that only one or two axles (and the included wheels) are in a track section during a given occupancy time. Obviously the more axles present in a track section the higher the probability that at least one axle would provide a satisfiactory shunt. Further the track circuits must be sensitive and fast in operation since a series of cars may be following one another in rather close succession and the command signals for each car must be initiated and transferred to the conice 1 2 Further, when dry weather conditions exist, a high voltage impressed across rails tends to over-energize the track relay as well as to create other undesirable conditions, such as affecting the operation of adjacent track circuits.

Accordingly, it is a principal object of my invention to provide a trackcircuit having a high shunting sensitivity.

It is another object of my invention to provide a track circuit including a relay having a fast shunt or release time and a slow pickup time.

It is another object of my invention to provide a trac circuit capable of shunting through high resistance film while utilizing a minimum of power.

In the attainment of the foregoing objects I provide a track circuit including, in one embodiment, a non-linear reactor having a primary winding and a secondary winding wound on an iron core. The primary winding is con nected in series with a capacitor to form a form-resonant circuit. The secondary winding is connected across the track rails to couple the reactor voltage to the track rails and reflects back to the primary winding, the resistance existing across the track rails. At a critical value of track rail resistance the ferro-resonant circuit is arranged to be tuned approximately to resonance and the reactor is arranged to saturate; this limits to a predetermined value the voltage impressed across the track rails and therefore the current coupled to an associated track relay. The track relay includes a first and second operating coil.

The second coil is connected to momentarily retard the build-up of a flux held in the magnetic circuit of the relay when the first coil is energized to delay the actuation of the relay contacts thus providing a time delay to th circuit.

Other objects and advantages of my invention will be come apparent from the following description and the accompanying drawing in which: FIG. 1 is a schematic diagram of the track circuit according to my invention; and

track circuit must include a track relay having a quick shunting but slow pickup characteristics.

It has been found that the characteristics of conventional track circuits are such that the current flowing in the track relay varies considerably from a operating value when the ballast resistance is low, to a maximum value when the ballast resistance ishigh. This makes it ditlicult to maintain the timing of the track relay at a relatively constant value, since the track relay when highly energized picks up quickly and when shunted releases rather slowly. It is known that greatly increased shunting sensitivity of a track circuit can be obtained by increasing the voltage impressed across rails since a high voltage tends to break down the nonconductive film to permit track circuit current to flow through the wheel and axle However, if a high voltage is steadily applied between the rails the track circuit power input tends to become excessive, especially under wet weather conditions when the ballast resistance is relatively low.

FIG. 2 is a graph useful in explaining the operation of my ferro-resonant circuit. j

Referring to the FIG. 1, the reference characters 11a and 11b designate track rails of a section of railway track 10 insulated by rail joints 13a and 13b from adjacent track sections. Power to track section 10 is supplied through a non-linear reactor 15 having a primary winding 17 and a secondary winding 19 wound on a saturable iron core. One terminal of primary winding 17 of reactor 15 is connected to any suitable alternating current source, for example, a -cycle, 115 volt source. The other terminal of primary winding 17 is connected through a capacitor 21 to the source. The primary winding 17 and capacitor 21 comprise a series ferro-resonant circuit as will be explained more fully hereinbelow. One terminal of the secondary winding 19 is connected through lead 23 to rail Hz: at one end, the left-hand end as oriented in FIG. 1, of the track section 10 and the other terminal of winding 19 is connected through E lead 25 to rail 11b at thesame end of track section 10.

pending upon the moisture, temperature, etc. Ashunt resistance on the track section 10. is indicated by the wheel and axle unit 16.

A transformer 31, having a primary winding 29 and a secondary winding 33 couples energy from the track rails 11a and 11b to a track relay 41. One terminal of primary winding 29 iscOnnected through lead 27 to rail 11a at the right-hand end of track section 10, as oriented in FIG. 1; and the other terminal of primary winding 29 is connected through lead 28 to track rail 11b also at the right-hand end of track section 10. Primary winding 29 includes a pair of intermediate taps 32 and 34 for permitting various connections to rails 11a and 11b for purposes explained hereinbelow. The secondary winding 33 of transformer 31 is connected across the two alternating current terminals 38 and 40 of a full-wave diode bridge rectifier 35 of the well known type. A direct current terminal 42 of rectifier 35 is connected through lead 36 and a variable resistor 37 to one end of an operating coil 39 of relay 41 which relay has a pair of operating coils 39 and 43. The other direct current terminal 44 of rectifier 35 is connected through lead 46 to the other end of coil 39. Relay 41 includes the usual stationary and movable contacts a.

A filtering capacitor 45 is connected across the two direct current terminals 42 and 44 of rectifier 35 to smooth out any ripple from rectifier 35.

A diode 47 is connected, with a polarity as shown in FIG. 1, across the second operating or delay coil 43 of relay 41, and a relatively high resistance resistor 49 is connected in parallel to diode 47. The diode 47 and resistor 49 effect a quick shunting but slow pickup action for the contacts of relay 41 as will be explained hereinbelow.

A lightning arrester 57 is desirably connected across leads 27 and 28 to protect the track relay 41 and the associated circuits from high voltage surges.

Ferro-resonant circuits are known in the art; one of the earlier discussions of such circuits is given in the article, Studies in Non-Linear Circuits, by C. G. Suits, published in June, 1931, issue of the Transactions of the American Institute of Electrical Engineers.

Essentially, a ferro-resonant circuit comprises an inductor wound on a saturable iron core which inductor is connected to a capacitor and across a source of alternating current potential. The inductor and the included iron core have a non-linear impedance characteristic which is the basis of the operation of the ferro-resonant circuit. 1

In several applications with which I am familiar ferroresonant circuits are employed to provide constant current or voltage output with a variable input voltage. In contrast, in the track circuit according to my invention, the source voltage is substantially constant and the resistance or impedance existing across the track rails controls the current supplied to an associated track relay.

The operation of my track circuit will be described with reference to the graph of FIG. 2 in which the axis of abscissa indicates the resistance existing across the track rails 11a and 11b, and the axis of ordinates indicates the current flowing in operating coil 39 of track relay 41. The current flowing through coil 39 is obviously proportional to the voltage existing across the track rails so that the axis of ordinates also indicates the voltage impressed across the track rails.

It can be seen from any standard text that the resistance appearing across the terminals of a secondary winding 19 of the non-linear reactor is reflected back to the primary winding 17. Thus, the ferro-resonant circuit in my track circuit includes the reflected resistance existing across the track rails, which resistance is effectively connected in parallel with primary winding 17. It is this resistance existing across the track rails 11a and 11b and which is reflected through the secondary winding 19 to the primary winding 17 which is a key factor in the operation of the ferro-resonant circuit.

As shown in the graph of FIG. 2, it has been found that as the resistance existing across the track rails 11a and 11b is increased, the voltage appearing across the rails and consequently the current flowing through the track relay 41 increases substantially'linearly up to a critical point of resistance, designated as point A on the graph. For values of resistance between zero and point A, the

inductive reactance is larger than the capacitive reactance, and the current through the circuit will lag the applied voltage. For a critical value of resistance indicated by point A the inductive reactance decreases to a value approximately equal to that of the capacitive reactance, approximately tuning the 'ferro-resonant circuit to resonance, causing the voltage appearing across the reactor to increase sharply, and saturate the reactor. At point A, the circuit is almost in series resonance; however, the resonance condition is unstable. Therefore the ferroresonant circuit passes almost instantaneously from one stable state with lagging current to a second stable state in which the inductive reactance is slightly less than the capacitive reactance and the circuit has a leading current. After the non-linear reactor 15 saturates the voltage across the reactor and thus the current through operating coil 39 of track relay 41 is maximum; any further increase in resistance has no appreciable effect on the voltage appearing across the reactor and consequently the current flowing through the track relay remains substantially constant.

The process is reversible; as the resistance is lowered the current flowing in relay 41 drops or steps down from a maximum value to a lower value below the knee of the curve shown on the graph of FIG. 2. The critical resistance varies slightly with the source voltage but the relay current above the critical resistance is essentially constant even with considerable variation in the source voltage.

When connecting the secondary winding 19 of reactor 15 to track rails 11a and 11b, the taps, either the ends of secondary winding 19 or intermediate taps 24 and 26 are selected so that the critical resistance is less than the minimum ballast resistance to be encountered. The critical resistance will be proportional to the square of the number of turns of secondary winding 19 connected across the track rails. For resistance above the critical resistance the voltage existing across the track rails will be proportional to the turns of secondary Winding 19 connected across the track rails. V

Taps 32 and 34- on transformer 31 permit changing the impedance of transformer 31 which impedance is proportional to the square of the number of turns connected across the track rails. Consequently, the relation between the load of transformer 31 and the critical re sistance remains constant.

In operation in classification yards the ferro-resonant circuit is adjusted such that for a given 'voltage and a ballast resistance of 23 ohms which is about the minimum resistance present in short detector track circuits in classification yards, sufiicient current is flowing through the relay 41 to maintain the coil 39 energized, see FIG. 2. Should a shunt resistance, such as the wheel and axle unit 16 which 'is normally in the 0 to 5 ohms range, enter track section 10, the effective resistance reflected back to the primary winding 17 of non-linear reactor 15 will decrease and consequently pass through the critical resistance point A toward zero and cause the current through the coil 39 of track relay 41 to decrease, thus deenergizing relay 41.

When the track circuit is shunted, the relatively large resistor 37 connected in series with the operating coil 39 of relay 41 provides a means of dropping the voltage in the circuit of coil 39, thus reducing the current flow through coil 39 so that relay 41 releases its contacts a relatively fast, say 0.06 second after the application of shunt 16, The reduction in current flow through coil 39 tends to induce a current in the coil 43 of relay 41, but the diode 47 is poled to block any current flow so that the coil 43 does not exert any appreciable snubbing effect when a shunt is applied across the track rails. The rela tively high resistance of resistor 49 is connected across diode 47 to prevent breakdown of the diode 47. p

1 Should the ballast resistance increase above 23'0hn'1s the eifective resistance reflected back to the primary winding'17 of reactor 15 will also increase; however, since the reactor 15 is already in saturation, any increase in resistance will not cause the voltage appearing across the track rails or the track relay current to increase; as indicated by the horizontal straight line portion of the graph of FIG. 2.

As noted above, slow pickup of the contacts a of track relay 41 is obtained by means of diode 47 connected in series with the second coil 43 of relay 41. When the shunt resistance is removed from the'track section the current flow through coil 39 increases and a current is induced in the second or delay coil 43 of relay 41. The current in coil 43 is practically short circuited by the diode 47. It can be considered that some of the energy required to build up a flux in the magnetic circuit, not shown, of relay 41 is required to produce a current in coil 43 and diode 47. Thus the build-up of a sufiicient field to attract the relay 41 armature, not shown, and thus to pick up relay contacts a is delayed for a period of time of from 0.4 to 0.5 second measured from the time the shunt resistance is removed until the time the relay contacts are actuated to pick up or close.

The capacitor 45 connected across the direct current terminals of rectifier 35 smooths out any ripple so that, after a stable condition is attained, diode 47 will not provide reverse current flow due to ripple.

Although I have herein shown and described only one formof apparatus embodying my invention, it will be understood that various changes and modifications may be made therein within the scope of the appended claims without departing {from the spirit and scope of my invention.

Having thus described my invention what I claim is:

1. A track circuit for a section of railway track having ballast resistance existing across the track rails comprising, in combination, a non-linear reactor including a primary winding and a secondary winding wound on a saturable core; a capacitor connected in series with said primary winding for forming a term-resonant circuit; a source of alternating current energy; means connecting said capacitor and said primary winding for receiving energy from said source; means connecting said secondary winding across said track rails for providing alternating current energy to said track rails; said secondary winding reflecting the resistance existing across said track rails back to said primary winding; said ferro-resonant circuit resonating at a critical value of I resistance reflected to said primary winding for developing a sufliciently high voltage across said primary winding to saturate said reactor; a transformer having a primary winding and a secondary winding,said primary winding of said transformer being connected across said track rails; a bridge rectifier having a pair of alternating current terminals and a pair of directcurrent terminals; said alternating current terminals of said rectifier being connected across said secondary winding of said transformer; a track relay including contacts,an operating coil and a delay coil mounted to be mutually inductive; said operating coil being connected across the direct current terminals of said rectifier; said operating coil being energized to pick up said relay contacts when the ballast resistance is equal to and larger than the critical resistance; said operating coil being decnergized to release said contacts when said track rails are shunted and the resistance across said track rails decreases to a value below the critical resistance; and, a diode connected across said delay coil with a polarity permitting an induced current to flow in said delay coil when current in said operating coil is increasing, whereby said delay coil delays the pickup of said relay contacts.

2. A track circuit for a section of railway track having ballast resistance existing across the track rails comprising, in combination, a non-linear reactor including a primary winding and a secondary winding wound on a satu r'able core; a capacitor connected in series with said primary winding for forming a ferro-resonant circuit, means connecting said capacitor and said primary winding for receiving energy from a source of alternating current; means connecting said secondary winding across said track rails for providing energy to said track rails; said secondary winding reflecting the resistance existing across said track'rails back to said primary winding; said ferroresonant circuit being tuned to resonate at a critical value of resistance reflected to said primary winding for developing a suificient-ly high voltage across said primary winding to saturate said reactor; the output voltage characteristics of said ferro-resonant circuit .being substantially linear for resistance values below said critical resistance, having a sharp stepped increase at said critical resistance resonant circuit and being substantially constant for resistance values above said critical resistance; a transformer having a primary and a secondary winding, said primary winding of said transformer being connected across said track rails; a bridge rectifier having a pair of alternating current terminals and a pair of direct current terminals; said alternating current terminals of said rectifier being connected across said secondary winding of said transformer; a track relay including contacts, an

operating coil and a delay coil mounted to be mutually inductive; said operating coil being connected across the direct current terminals of said rectifier; said operating coil being energized to pick up said contacts when the ballast resistance is equal to and larger than the critical resistance, said operating coil being dcenergized to release said contacts when the ballast resistance is shunted and the resistance across said track rails falls to a value below the critical resistance; and a diode connected across said delay coil with a polarity permitting an induced current to flow in said delay coil when current in said operating coil is increasing, whereby said delay coil delays the pickup of said relay contacts.

3.. A track circuit for a section of railway track having resistance existing across the track rails comprising, in combination, a non-linear reactor including a primary winding and a secondary winding Wound on a saturable core; a capacitor connected in series with said primary winding for forming a ferro-resonant' circuit; means connecting said. capacitor and said primary winding for receiving energy from a source of alternating current; one terminal of said secondary winding being connected to one of the track rails and the other terminal of said secondary winding being connected to the other track rail; said secondary winding reflecting the resistance existing across said track rails back to said primary winding; said primary winding and said capacitor being tuned to resonance at a critical value of resistance reflected to said primary winding for developing a sufficien-t voltage across said primary wind-ing to saturate said reactor; the voltage characteristics of said ferro-resonant circuit being substantially linear for resistance values below said critical value, having a sharp stepped increase at said critical value, and being substantially constant for resistance values above said critical value; a transformer having a primary winding and a secondary winding, one terminal of the primary winding of said transformer being connected to one rail and the other terminal of said primary winding of said transformer being connected to the other rail; a full-wave bridge rectifier having a pair of alternating current terminals and a pair'of direct current terminals; said alternating current terminals of said rectifier being connected across said secondary winding of said transformer; a track relay including contacts, an operating coil and a delay coil mounted to be mutually inductive; one of the direct current terminals of said rectifier being connected to one end of said operating coil and the other direct current terminal of said rectifier being connected to the other end of said operating coil; said operating coil being energized to pick up said contacts when the resistance across said track rails is at and above the critical resistance said track rails decreases below said critical value; and a diode connected across said delay coil, an increase in current flow through said operating coil causing a current to be induced and flow through said coil and said diode which delays the pickup time of said relay.

4. A track circuit for a section of railway track having resistance existing across the track rails comprising, in combination, a track relay including an operating coil; a non-linear reactor including a primary winding and a secondary winding wound on a saturable core; a capacitor connected in series with said primary winding for forming a ferro-resonant circuit; means for connecting said capacitorand said primary winding to receive energy from an alternating current source; means connecting said secondary winding across said track rails for coupling alternating current energy thereto; said secondary winding reflecting the resistance existing across said track rails back to said primary winding; said ferro-resonant circuit being tuned to resonate at a critical value of resistance reflected to said primary winding for developing a sufliciently high voltage across said primary winding to saturate said reactor; the output voltage characteristics of said ferro-resonant circuit being substantially linear for resistance values below said critical reistance, having a sharp stepped increase at said critical resistance, and being substantially constant for resistance values above said critical resistance; and means for coupling current energy from said track rails to said track relay; the current flowing through said track relay corresponding to the output voltage characteristics of said ferro-resonant circuit.

5. A track circuit for a section of railway track having ballast resistance between the track rails comprising, in combination, a track relay including an operating coil; a non-linear reactor including a primary winding and a secondary winding wound on a saturable core; a capacitor connected in series with said primary winding for forming a ferro-resonant circuit; means connecting said ferro-resonant circuit for receiving energy from a source of alternating current energy; means connecting said secondary winding across said track rails for coupling energy thereto, said secondary winding reflecting the resistance existing across said track rails to said primary winding, transformer means coupling energy from said track rails to said track relay operating coil, the voltage appearing across said track rails and current flowing through said track relay initially varying linearly as the resistance reflected back by said secondary winding to said primary winding increases, said ferro-resonant circuit be ing tuned to resonate at a critical value of resistance reflected to said primary Winding for developing a sumciently high voltage across said primary winding to saturate said reactor, the current flowing through said track relay increasing sharply to a maximum operating value when said ferro-resonant circuit is in resonance, and the saturation of said core limiting the current flowing in said track relay irrespective of any increases of the ballast resistance above said critical value of resistance.

6. A track circuit for a section of railway track having ballast resistance existing between the track rails comprising, in combination, a non-linear reactor having a primary winding and a secondary winding Wound on an iron core; a capacitor connected in series with said primary winding for forming a ferro-resonant circuit; means for connecting said -ferro-resonant circuit to receive alternating current energy; means for connecting said secondary winding across the track rails for providing energy to the track rails; said secondary winding reflecting the ballast resistance to said primary winding; said ferro-resonant circuit being tuned to resonate at a critical value of resistance reflected to said primary winding for developing a sufliciently high voltage to saturate said reactor for providing a limited maximum voltage to the track rails; said critical value of resistance being less than the minimum value of ballast resistance reflected to said primary winding; a

8 track relay; means for coupling voltage from the trackrails to operate said track relay; and means for adjusting said relay to release when the track rails are shunted and the resistance existingacross said track rails decreases below said critical value of resistance.

7. A track circuit for a section of railway track having the resistance existing thereacross comprising, in combination, a saturable reactor having primary and secondary windings, capacitor connected to said primary winding for forming a ferro-resonant circuit, means connecting said ferro-resonant circuit for receiving alternating current energy, means connecting said secondary winding across said track rails for coupling energy to said track rails, said secondary winding reflecting the resistance existing across said track rails to said primary winding, a track relay, and means for coupling current energy from the track rails to said track relay, said ierro-resonant circuit tuned to resonate and said core arranged to saturate at a critical value of resistance reflected back to said primary winding whereby the current coupled from said track rails to said track relay is limited to a maximum value.

8. A track circuit for a section of railway track having resistance existing thereacross comprising, in combination, a track relay including an operating coil; a

non-linear reactor including a primary winding and a secondary winding wound on a saturable core; a capacitor connected to said primary winding for forming a ferroresonant circuit, means for connecting said capacitor and said primary winding across a source of alternatingcurrent energy, means for connecting said secondary winding across said track rails for providing energy thereto, said secondary Winding reflecting the resistance existing across said track rails to said primary winding, said ferroresonant circuit being tuned to resonate at a critical value of resistance reflected to said primary Winding for providing a sufficiently high voltage to saturate said core, and transformer means for coupling energy from said track rails to said track relay operating coil, said core when saturated limiting the energy coupled through said reactor to said track relay operating coil.

9. A track circuit for a section of railway track having resistance existing between the track rails comprising, in combination, a non-linear reactor including a primary winding and a secondary winding wound on a saturable core; a capacitor connected to said primary winding for forming a ferro-resonant circuit, means for connecting said capacitor and said primary winding across an alternating current source, means for connecting said secon dary winding across said track rails for providing a volt age to said track rails, said secondary winding reflecting the resistance existing across said track rails to said primary winding, said ferro-resonant circuitbeing tuned to resonance at a critical value of resistance and providing a voltage across said primary winding suflicient to saturate said core for limiting the maximum voltage applied by said reactor to said track rails, a track relay, and trans-- former means for coupling the voltage exising across said track rails to operate said track relay. 10. A track circuit for a section of railway track having resistance existing across the track rails comprising, in combination, a track relay, a non-linear, reactor including a primary winding and a secondary winding wound on a saturable core; a capacitor connected to said primary winding, means for connecting said capacitor and said primary winding across an alternating current energy source; means connecting one terminal of said secondary winding to one of said track rails and means connecting the other terminal of said secondary winding to the other of said track rails for supplying energy to said track rails; said secondary winding reflecting the resistance existing across the track rails to said primary winding, said primary winding and said capacitor being tuned to resonance at a critical value of resistance existing across said track rails, said core being saturated when and transformer means for coupling energy from said track rails to said track relay, said core when saturated limiting the maximum energy coupled through said reactor and the track rails to said track relay.

11. A track circuit for a section of railway track having resistance existing between the track rails comprising, in combination, a ferro-resonant circuit including a winding wound on an iron core and a capacitor connected to said winding, said term-resonant circuit being connected in series withan alternating current source of energy; means connecting said ferro-resonant circuit and said source across said track rails for providing a voltage thereto; said ferro-resonant circuit being tuned to resonate at a critical value of resistance existing across said track rails for reveloping a sufficiently high voltage to saturate said core for limiting the maximum voltage provided to the track rails; said critical value of resistance being less than the minimum value of resistance existing between the track rails; a track relay; means for coupling 20 12. A track circuit for a section of railway track having resistance existing thereacross comprising, in combination. a ferro-resonant circuit comprising a winding wound on an iron core and a capacitor connected to said Winding, said ferro-resonant circuit being connected in series with an alternating current source of energy, means connecting said ferro-resonant circuit and said source across said track rails for providing a maximum voltage thereto, said ferro-resonant circuit aranged to resonate at a critical value of resistance existing across said track rails for developing a sufiicient voltage across said winding to saturate said core, a track relay, means for coupling energy from the track rails to said track relay whereby the current coupled from said track rails to saidtrack relay is limited to a maximum value.

References Cited in the file of this patent UNITED STATES PATENTS 2,061,747 Witmer et al. Nov. 24, 1936 2,4211148 Hadfield May 27, 1947 FOREIGN PATENTS 734,573 Great Britain Aug. 3, 1955 

